The present invention concerns a nuclear radiation metallic absorber, more particularly an absorber containing a copper metallic alloy with 0.05 to 50% boron in weight compared to the total alloy weight. The ever increasing use of nuclear energy worldwide together with the development of nuclear techniques in general requires protections against the nuclear radiations (nuclear power stations, transportation and storing of radioactive waste, nuclear machines . . . ). It is therefore of prime importance and necessity to design and produce efficient and competitive radiation absorbers.
The absorption material is to comply with the following criterions:
First of all it must have specific nuclear properties: high neutron absorption cross section, low secondary radiation emission, and long duration stability against radiation.
It must have a high melting point to resist the heat released by absorption of radiation and more specifically by the neutron flux.
It must be a good heat conductor to facilitate cooling.
The residual heat must be within not too high limits (released as radiation after the stop).
Its mechanical resistance must be high enough.
It must resist corrosion by the coolant or the working atmosphere.
It must have a good heat and radiation resistance.
Its price must be competitive both with regard to the raw material and processing.
All elements are more or less good radiation absorbers, but those having the most outstanding neutron absorbing properties are: cadmium, boron, europium, hafnium, gadolinium, samarium and dysprosium.
Cadmium has the drawback of being highly toxic for the human body and its use is strictly prohibited in many countries. Moreover both its melting point (321.degree. C.) and bviling temperature (761.degree. C.) are very low, and its corrosion resistance in aqueous medium is very poor.
Europium and dysprosium although endowed with a big efficient absorbing section are seldom employed due to their very high price.
The absorbing properties of hafnium are much lower than those of boron with regard to thermal and epithermal neutrons, its price is high and its processing delicate due to its oxidizability.
Gadolinium shows in the thermal neutron spectrum the highest efficient absorbing section of all known absorbers. It can be seen, for example, that its efficient absorbing section is approximately 100 times higher than that of boron with regard to neutrons having an initial energy of 10.sup.-1 to 10.sup.-3 electron-volts. Unfortunately in the area of epithermal neutrons and slow neutrons (energy of 0.3 to 10.sup.2 electron-volts) the absorption properties are considerably below those of boron.
The gadolinium oxide has been used for many years in various nuclear installations where, when blended with the fuel, it plays the role of the moderator. But problems arise when gadolinium oxide is used for the production of radiation absorbers. Indeed the oxide which is generally available as powder must be mixed with other products which requires a very complex technology. When producing absorbers having a complex shape its poor mechanical properties result in critical and expensive processes. Moreover this oxide has a poor thermal conductivity and its absorption capacity is relatively reduced compared to that of elementary gadolinium.
Samarium has interesting neutron absorbing properties intermediate between those of boron and gadolinium with regard to thermal neutrons, and superior to boron and gadolinium with regard to intermediate and fast neutrons.
However compared to boron two areas of weak absorption remain, the first between 1 and 5 eV, the second between 30 and 40 eV. The most widespread absorber and best known for the criticity calculations is without any doubt boron which is used in various forms: elementary boron, borides (aluminum, chromium, hafnium, molybdenum, niobium, tantalum, titanium, tungsten, vanadium, zirconium . . . ), boron carbide, boron oxide B.sub.2 O.sub.3, boron nitride, boric acid, borax etc. Processing of all the materials presently marketed is critical: the elementary boron has poor mechanical properties, and its thermal conductivity is low (32 W/m.degree.K.). At high temperatures it is highly oxidizable and its corrosion resistance is poor. It must be inserted as a chemical component defined in various matrices and such composite material results in homogeneity and processing problems.